1. Field of the Invention
The present invention relates, generally, to a liquid deionizing system and, more specifically, to liquid deionizing twin bed apparatus of the type used in connection with a pressure vessel having an inlet for receiving untreated ionized liquid and an outlet through which the treated deionized liquid exits the vessel.
2. Description of the Related Art
Deionizing systems remove impurities from liquid such as water. Today, much of the municipal and well water used by residential and commercial consumers is termed "hard" because it contains certain mineral salts and metals. Certain consumers, for example soft drink and alcohol manufacturers, must purify the water used in their products. In addition, the demand for purified water among individual consumers is also growing. Furthermore, hard water creates problems beyond human consumption. The dissolved metals give the water a significant level of conductivity. Certain industrial applications, for example, coolants for electrical discharge machinery, require water with extremely low levels of conductivity. Water deionizing systems remove these impurities.
These systems typically include a pressure vessel that houses polystyrene ion exchange materials in the form of small beads. Exchange materials are generally of two types: anionic and cationic. Anionic exchange materials are given a positive charge and cationic exchange materials are given a negative charge. When a liquid such as ionized water is run through the pressure vessel, the beads react with the water and bond with the impurities. In turn, the exchange materials release hydrogen and oxygen resulting in extremely pure water. After a certain amount of time, however, the exchange materials become "full" or "spent" and lose the ability to remove impurities. At this point, the anionic and cationic exchange materials must go through a process called regeneration.
During regeneration, one type of exchange material is subjected to an acid, and the other is subjected to a caustic. This strips the beads of the respective exchange materials of "bad" chemicals and reapplies hydrogen and oxygen ions. This process normally takes place at regularly scheduled intervals. The amount of time between regeneration cycles depends on the purpose for which the deionizing system is employed. For example, in heavy industrial use in an EDM environment, the exchange materials may require regeneration every one to two weeks. Other water purifying environments may require regeneration once a month or at longer intervals.
Anionic and cationic exchange materials require different regenerating agents. Where the treatment of liquids requires the use of two or more exchange materials which must be regenerated with different regenerating agents, the different exchange materials are sometimes placed in separate pressure vessels. These vessels are then connected in fluid communication with each other. Raw water is delivered to the tank housing anion exchange materials. The water passes through the tank and is then delivered to the second tank housing cation exchange materials. Once the water has passed through the second tank, it is purified and ready for use. Keeping exchange materials in separate, homogeneous groups is known in the art as a "twin bed."
Unfortunately, connecting several pressure vessels in series can require a great deal of hardware, plumbing and technical effort. When the exchange materials are spent and require regeneration, the vessels must be disconnected from the system, removed and taken to a regeneration facility. It is relatively costly to remove, transport, and reinstall several pressure vessels every time regeneration is needed. Thus, there was a demand in the related art to provide a single pressure vessel which housed both anionic and cationic exchange materials which would thereby reduce the labor and overall cost of exchanging pressure vessels.
The use of different exchange materials requiring different regeneration agents mixed together within a single pressure vessel is known in the art as a "mixed bed." Pressure vessels employing mixed beds eliminated the need for, and expenses associated with, multiple vessels. However, it is still costly to remove, transport, and reinstall even one pressure vessel when regeneration is needed. Therefore, it became known to house exchange materials within the pressure vessel in a liquid permeable container. When regeneration is necessary, the container is removed from the pressure vessel and taken to the regeneration facility. This practice again reduced labor efforts associated with regeneration, saving time and money. At the same time, it should be noted that mixed bed deionizing systems have 20-30% shorter useful lives when compared with twin bed systems.
Although mixed beds and removable liquid permeable containers were considered an improvement in the related art, there is still a major cost associated with regeneration. When mixed beds are employed, the anionic and cationic exchange materials must be manually separated into homogeneous groups before they can be regenerated. The labor associated with the separation of exchange materials now represents the single largest expense in the regeneration of mixed beds.
In an effort to overcome the cost disadvantage associated with the regeneration of mixed beds, regeneration of the exchange materials within the pressure vessel itself has been proposed. For example, U.S. Pat. No. 4,400,278 issued to Martinola discloses a countercurrent water treatment tank. The Martinola '278 treatment tank operates using two or more exchange materials which are regenerated with different agents within the tank itself. More specifically, Martinola discloses that the loading of the different absorbents (exchange materials) is effected in a stream of liquid flowing upward and regeneration of the different spent absorbents using different regeneration agents is effected in a stream of liquid flowing downward. The Martinola treatment tank is subdivided into a number of chambers corresponding to the number of different absorbents used. Each of the chambers are equipped with a liquid drainage system which is located below the device which is permeable to liquid and forms the upper boundary of the chamber and which is embedded in a layer of inert material. The spent regenerating agent and washing water are removed via the liquid drainage system of the chamber below simultaneously with a stream of water which flows in counter-current to the stream of spent regenerating agent and washing water and which is being passed from the bottom upwards through this very chamber below. However, the Martinola '278 water treatment tank suffers from the disadvantage that it is relatively complex, requiring sophisticated internal plumbing and controls and is therefore relatively expensive.
Thus, there remains a need in the art to house different exchange materials requiring different regenerating agents in a single pressure vessel with a relatively simple structure while at the same time keeping those different exchange materials in twin beds (homogeneous groups) in order to minimize labor costs associated with regeneration.